1. Field of the Invention
The present invention relates to an ultrasonic bonding method of an electric wire in which ultrasonic bonding of a conductor part of the electric wire made of plural core wires is performed to a metallic terminal.
2. Description of the Related Art
An ultrasonic bonding method is known conventionally as a method for connecting a conductor part of an electric wire to a metallic terminal. As one example of this ultrasonic bonding method, for example, a method in which an electric wire in which a conductor end made of plural core wires is exposed from an insulating outer skin and a connection terminal formed by erecting two side walls from a bottom surface are prepared and after the conductor end of the electric wire is first molded by press in a flat shape (flat plate shape), ultrasonic vibration is applied while this conductor end molded by press is positioned in the bottom surface between the two side walls of the connection terminal and is pushed by a horn and thereby, the conductor end is bonded to the connection terminal is disclosed (see Patent Reference 1). Consequently, properties of adhesion between the connection terminal and the conductor end molded by press are ensured, so that good bonding properties can be obtained.    Patent Reference 1: JP-A-2006-172927
Incidentally, according to Patent Reference 1, the conductor end is molded by press by being pressurized from a thickness direction in a state of regulating a width according to a dimension between the side walls of the connection terminal. As a result of this, the conductor end set in the connection terminal is pinched between the side walls and is supported. On the other hand, in the horn, a dimension of a width direction between the side walls is set smaller than a dimension of a width direction of the conductor end in order to prevent contact with the side walls at the time of applying pressure and vibration to the conductor end.
When such a horn is pushed on the conductor end set between the side walls of the connection terminal and ultrasonic vibration is applied, the conductor end is pushed on the horn and becomes deformed so as to spread in the width direction between the side walls and the core wires of the sides of the side walls become pushed on the side walls. When further application of ultrasonic vibration is continued, the core wires pushed on the side walls swell along the side walls and may reach a position higher than the upper ends of the side walls. The core wires swelling to the position higher than the side walls thus, for example, tend to become an obstacle in the case of insertion into a housing into which the connection terminal is inserted, and may also cause electrical trouble such as a short circuit in the case of having a deficiency of the core wires.